PROJECT SUMMARY/ABSTRACT Most existing work on adolescent development has focused on risk and psychopathology, as opposed to more positive developments, such as prosocial behavior. This previous focus is unfortunate given that prosocial behavior has been linked with a variety of positive health outcomes across a wide age range, including in childhood and adolescence. Given these observed health benefits of prosocial behavior, an increased focus on the neurobehavioral developments that underlie prosocial behavior during adolescence is warranted. The proposed work will examine developmental differences in prosocial behavior, specifically examining underlying neural mechanisms of prosocial behavior that may contribute to observed health outcomes. This will be done by linking neurobehavioral correlates of prosocial behavior with interferon-gamma (IFN-g), an important marker of antiviral immunity. The objective of this NRSA application is to foster my development as a social neuroscientist investigating the impact of social phenomena on health across development. To do so, the proposed study will 1) examine developmental differences in prosocial behavior, 2) characterize the neural underpinnings of prosocial behavior, and 3) examine associations between IFN-g and prosocial behavior across development. Prosocial behavior will be examined via reinforcement learning models, which can provide a measure of motivation or intention to act prosocially. Participants (ntotal=120; children [9-10 yr], adolescents [14-15 yr], young adults [19- 20 yr]) will complete a probabilistic learning task in which they learn contingencies via positive and negative reinforcement in order to earn money for themselves (self learning) and a friend (prosocial learning), while undergoing a functional magnetic resonance imaging (fMRI) scan. A subset of subjects will complete a blood draw to assess IFN-g. Increased reward sensitivity, which is associated with greater adolescent well-being, has been shown to facilitate reinforcement learning generally. Thus, adolescent reward sensitivity may promote prosocial learning?learning in order to benefit someone else. It is therefore predicted that 1) adolescents will have better prosocial learning rates relative to adolescents? self learning rates and relative to children/young adults? prosocial learning rates. Additionally, given the proposed reward-based mechanism of prosocial learning, it is hypothesized that 2) increased striatal activity will mediate the predicted developmental differences in prosocial learning rates, such that adolescents will have the best prosocial learning rates due to increased prediction error-related striatal activity. Finally, it is predicted that 3) higher IFN-g will be associated with better prosocial learning and greater prediction error-related striatal activity during prosocial learning. The present study will help to elucidate underlying neural and immunological correlates of prosocial behavior across development, leading to a better understanding of observed health benefits and their developmental trajectory.